An attempt was made to develop an animal model for Intra Uterine Growth Retardation (IUGR) in the mouse. Superovulation produced approximately twice the number of embryos in the mouse and produced significant crowding and competition for maternal nutrients and oxygen. Partial hemioophorectomy was performed in some animals to attempt intra-animal comparisons. The results of these experiments suggest that superovulation may be an easy, quick and inexpensive method of achieving IUGR in mice.